Is sleeping on your back safe during pregnancy?

What does the evidence say about sleeping on your back during pregnancy?

1. A large New Zealand study linked falling asleep on your back in late pregnancy to a nearly fourfold higher chance of stillbirth, accounting for an estimated 9 percent of cases, which led researchers to recommend a public campaign promoting side-sleeping in the third trimester. 1
2. Lying flat on your back late in pregnancy lets the heavy uterus press on a major vein, which measurably reduces blood flow back to your heart. 2
3. A Sydney study found an even higher risk with back-sleeping, over six times higher odds of stillbirth, but noted this mainly added risk on top of a pregnancy where the baby was already growth-restricted or otherwise vulnerable, rather than causing harm on its own in an uncomplicated pregnancy. 3
4. A study across the Midlands and North of England found a smaller but still real increase in risk, about 2.3 times higher odds of stillbirth for back-sleeping versus left-side sleeping, a reminder that sleep position is one factor among several, not the main driver of stillbirth. 4
5. Most women who heard New Zealand's side-sleeping campaign were able to change their habit without extra worry: a follow-up survey found 86.5 percent had received the advice, two-thirds changed their habit, and 90.4 percent said it didn't add anxiety. 5

Is sleeping on your back safe in each trimester?

• First trimester. Early on, your uterus is still low and light, so it doesn't press on major blood vessels yet. Back-sleeping hasn't been linked to added risk at this stage, so sleep however feels most comfortable and lets you rest.
• Second trimester. As your uterus grows, lying flat starts to feel less comfortable for many people, even before it matters medically. That's a good natural cue to start practicing side-sleeping now, ahead of the third trimester when it counts more.
• Third trimester. From about 28 weeks on, studies have found a higher chance of late stillbirth when women fall asleep on their back compared with their side, so aim to fall asleep on either side from now on. The research looked at the position women fell asleep in, not every shift overnight, so waking up on your back briefly and rolling over is nothing to worry about.